If there is no veil of darkness how can there be misery?
If it is natural characteristic of the life, when there is a
substance that will remove the misery, the life would also be destroyed.

Notes:

1. The philosophical works deal with three substances and
their inter-relationship. The three substances are God, life
and material. Some philosophies (like Buddhism) say none
are real and it is void or sunya ultimately. Some other atheistic
schools say only material is evident and hence life and God are
false. Some others like Ekatmavada say only God is real and
rest is all aberration. There are so many combinations this way.

Shaiva Siddhanta establishes that all the three are real
and the relationship among them changes in a positive direction.
The creation is a mechanism God devised to implement
this positive change.

In this song Umapathi Sivam is establishing that the
material substance of veil of darkness is real.

2. If we assume that there was no veil of darkness,
how will one explain the misery that the life undergoes?

God, being the Limitless Mercy, cannot be inflicting
misery on the life, as it would put in question the
Limitless Mercy of God.

The other option is to put it on the life itself saying,
"Misery is the character of the life." If this is the case,
at the ultimate state of Eternal Bliss, where due to
intervention of some substance (God), the misery of the life
is wiped off, the life also should get destroyed, as misery is
its own natural character and it goes away along with the misery.

Hence it can be derived that there is a substance that
causes misery to the life, which is different from both God and life.
It is the veil of darkness.